Method for preparing epoxypropane by catalyzing propylene air epoxidation through double metal-free catalysts
By using a combination of a dual metal-free catalyst and a reducing agent, and employing air as the oxidant, the problems of high cost and low selectivity of metal catalysts in existing technologies are solved, achieving efficient and low-cost propylene oxide preparation, which has good prospects for industrial application.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHEJIANG UNIV OF TECH
- Filing Date
- 2026-01-20
- Publication Date
- 2026-05-19
AI Technical Summary
In existing technologies, the production of propylene oxide by catalytic metal catalysts is costly, has low selectivity, and is prone to the generation of byproducts, posing safety risks. Moreover, most of these processes are complex and make it difficult to achieve efficient and low-cost propylene oxide production.
Using a dual-metal-free catalyst and reducing agent, and air as the oxidant, propylene is catalyzed to produce propylene oxide under specific conditions. This avoids the use of metal catalysts, employs a green oxidant, reduces costs, and improves the activity and selectivity of the reaction.
It achieves a propylene conversion rate of up to 10-95% and a propylene oxide selectivity of up to 60-99%, avoiding equipment corrosion and environmental pollution, and has good prospects for industrial application.
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Figure CN122059908A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of homogeneous catalysis technology, specifically to a method for preparing propylene oxide by air epoxidation catalyzed by dual metal-free catalysts. Background Technology
[0002] Propylene oxide (PO) is the third largest derivative in the propylene industry and can be used to manufacture a variety of important products, such as polyurethane foam for the automotive and housing industries, polyester resins for the textile and construction industries, and propylene glycol as an ingredient in pharmaceuticals, cosmetics, and heat transfer or hydraulic oil additives. The production of PO from propylene is a key process in the chemical industry. Over the past few decades, PO production processes have shifted from chlorohydrinization to direct oxidation and co-oxidation processes.
[0003] Direct oxidation methods are divided into hydrogen peroxide and oxygen oxidation methods. The hydrogen peroxide method has poor stability and low safety; the oxygen method is still in the basic research stage. Co-oxidation methods (such as ethylbenzene, isobutane, and cumene methods) prepare organic peroxides by activating CH bonds, and then oxidize propylene to produce PO, which is more in line with the theme of green chemistry. Currently reported catalysts are mainly metal catalysts (such as Au and Ag), which are expensive, have low selectivity, and are prone to over-oxidation of propylene to byproducts such as acetone and CO2. The active centers are prone to sintering or deactivation at high temperatures. In most high-efficiency systems, they require H2 / O2 mixtures or high-purity oxygen, which increases the complexity of the process and safety risks. In addition, metal leaching may also contaminate the product.
[0004] Therefore, developing a novel propylene epoxidation process with dual metal-free catalysis, mild conditions, low cost, and high yield is of great significance for promoting the industrial production of propylene oxide and expanding its applications in various fields. Summary of the Invention
[0005] The primary objective of this invention is to overcome the problem of low propylene oxide yield in the prior art by using a dual metal-free catalyst and reducing agent, with green and environmentally friendly air as the oxidant, to efficiently prepare propylene oxide.
[0006] Therefore, the technical solution provided by this invention is as follows:
[0007] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst involves dispersing the dual metal-free catalyst and a reducing agent in a solvent, sequentially introducing propylene and air at 1-6.0 MPa in a closed system, and reacting at a set temperature of 40-120 °C for 1-9.0 h to obtain the product propylene oxide.
[0008] The total molar amount of the dual metal-free catalyst and the molar ratio of propylene are 0.1-1:1-6.0.
[0009] The molar ratio of reducing agent to propylene is 5-15:1-10.
[0010] Furthermore, in the above-mentioned method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst, the metal-free catalyst is any two of the compounds having the following structures;
[0011] .
[0012] Furthermore, in the above-mentioned method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst, the reducing agent is one or two of acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, propionaldehyde, glutaraldehyde, n-hexanaldehyde, cyclohexeneformaldehyde, and benzaldehyde.
[0013] Furthermore, in the above-mentioned method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst, the reaction temperature is 95-120 °C.
[0014] Furthermore, in the above-mentioned method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst, the total molar amount of the dual metal-free catalyst and the molar ratio of propylene are 0.3:3.5-6.0.
[0015] Furthermore, in the above-mentioned method for preparing propylene oxide by air epoxidation of propylene using a dual metal-free catalyst, the molar ratio of the reducing agent to propylene is 9.5-12:3.5-6.0.
[0016] Furthermore, in the above-mentioned method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst, the reaction pressure is 2 MPa.
[0017] The method for analyzing the reaction results in this invention is as follows: After the reaction is complete, an appropriate amount of the reaction solution is taken for analysis. Using biphenyl as an internal standard, gas chromatography analysis is performed to calculate the conversion rate of propylene and the selectivity of propylene oxide.
[0018] Compared with the prior art, the present invention has the following beneficial effects:
[0019] 1. The technical solution provided by this invention uses air as an oxidant in the propylene epoxidation reaction, which avoids serious equipment corrosion, environmental pollution and safety problems caused by peroxy acids, peroxides, etc., and has good prospects for industrial application.
[0020] 2. The technical solution provided by the present invention uses a dual metal-free catalyst and a synergistic reducing agent to catalyze the epoxidation of propylene to prepare propylene oxide. The reaction has good activity and selectivity, with a propylene conversion rate of up to 10-95% and a propylene oxide selectivity of up to 60-99%. Attached Figure Description
[0021] Figure 1 This is the chromatogram of the product obtained by online sampling and gas chromatography analysis in Example 2;
[0022] Figure 2 These are the UV spectra of different reaction conditions in Example 2;
[0023] Figure 3 These are infrared spectra of different reaction conditions in Example 2. Detailed Implementation
[0024] The preferred embodiments of the present invention will now be described in detail so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.
[0025] Example 1
[0026] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0027] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following were added sequentially: a metal-free catalyst, N-hydroxysuccinimide (0.15 mmol), 4-nitro-2-methylpyridine-N-oxide (0.15 mmol), a reducing agent, n-butyraldehyde (9.5 mmol), an internal standard, biphenyl (50.0 mg), a solvent, acetonitrile (20.0 mL), and propylene (6.0 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 100 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 82%, and the propylene oxide selectivity was 99%.
[0028] The structural formulas of the dual metal-free catalysts N-hydroxysuccinimide and 4-nitro-2-methylpyridine-N-oxide are as follows:
[0029]
[0030] Example 2
[0031] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0032] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following were added sequentially: metal-free catalyst N-hydroxysuccinimide (0.15 mmol), azobisisobutyronitrile (0.15 mmol), reducing agent n-butyraldehyde (12.0 mmol), internal standard biphenyl (50.0 mg), solvent acetonitrile (20.0 mL), and propylene (4.0 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 95 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. (See reference...) Figure 1 The propylene conversion rate was measured to be 47%, and the propylene oxide selectivity was 99%.
[0033] The structural formulas of the dual metal-free catalysts N-hydroxysuccinimide and azobisisoheptanenitrile are as follows:
[0034]
[0035] Example 3
[0036] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0037] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following metal-free catalysts were added sequentially: N-hydroxysuccinimide (0.15 mmol), N-(hydroxymethyl)phthalimide (0.15 mmol), reducing agent n-butyraldehyde (9.5 mmol), internal standard biphenyl (50.0 mg), solvent acetonitrile (20.0 mL), and propylene (6.0 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 81%, and the propylene oxide selectivity was 99%.
[0038] The structural formulas of the dual metal-free catalysts N-hydroxysuccinimide and N-(hydroxymethyl)phthalimide are as follows:
[0039]
[0040] Example 4
[0041] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0042] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following were added sequentially: a metal-free catalyst, N-hydroxysuccinimide (0.15 mmol), succinimide (0.15 mmol), a reducing agent, n-butyraldehyde (10.7 mmol), an internal standard, biphenyl (50.0 mg), a solvent, acetonitrile (20.0 mL), and propylene (3.5 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 100 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 46%, and the propylene oxide selectivity was 98%.
[0043] The structural formulas of the dual metal-free catalysts N-hydroxysuccinimide and succinimide are as follows:
[0044]
[0045] Comparative Example 1
[0046] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0047] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following were added sequentially: a metal-free catalyst, N-hydroxysuccinimide (0.5 mmol), a reducing agent, propionaldehyde (4.0 mmol), an internal standard, biphenyl (50.0 mg), a solvent, acetonitrile (20.0 mL), and propylene (8.0 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 34%, and the propylene oxide selectivity was 98%.
[0048] The metal-free catalyst N-hydroxysuccinimide has the following structural formula:
[0049]
[0050] Comparative Example 2
[0051] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0052] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, 0.5 mmol of 4-nitro-2-methylpyridine-N-oxide (a metal-free catalyst), 3.5 mmol of propionaldehyde (a reducing agent), 50.0 mg of biphenyl (an internal standard), 20.0 mL of acetonitrile (a solvent), and 7.0 mmol of propylene were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 28%, and the propylene oxide selectivity was 96%.
[0053] The metal-free catalyst 4-nitro-2-methylpyridine-N-oxide has the following structural formula:
[0054]
[0055] Comparative Example 3
[0056] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0057] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, azobisisobutyronitrile (2.5 mmol) (a metal-free catalyst), propionaldehyde (7.25 mmol) (reducing agent), biphenyl (50.0 mg) (internal standard), acetonitrile (20.0 mL) (solvent), and propylene (6.5 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 26%, and the propylene oxide selectivity was 96%.
[0058] The structure of the metal-free catalyst azobisisoheptanenitrile is as follows:
[0059]
[0060] Comparative Example 4
[0061] The establishment of a dual metal-free catalytic method and its application in propylene air epoxidation includes the following steps:
[0062] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following were added sequentially: a metal-free catalyst, N-(hydroxymethyl)phthalimide (0.2 mmol), a reducing agent, n-pentanal (9.5 mmol), an internal standard, biphenyl (50 mg), a solvent, acetonitrile (20 mL), and propylene (4.75 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 30%, and the propylene oxide selectivity was 96%.
[0063] The metal-free catalyst N-(hydroxymethyl)phthalimide has the following structural formula:
[0064]
[0065] Comparative Example 5
[0066] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0067] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, succinimide (2.5 mmol) (metal-free catalyst), propionaldehyde (11.0 mmol) (reducing agent), biphenyl (50.0 mg) (internal standard), acetonitrile (20.0 mL) (solvent), and propylene (12.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 31%, and the propylene oxide selectivity was 96%.
[0068] The metal-free catalyst succinimide has the following structural formula:
[0069]
[0070] Comparative Example 6
[0071] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0072] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, 1.0 mmol of dilauryl peroxide (a metal-free catalyst), 5.5 mmol of propionaldehyde (a reducing agent), 50.0 mg of biphenyl (an internal standard), 20.0 mL of acetonitrile (a solvent), and 8.5 mmol of propylene were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 25%, and the propylene oxide selectivity was 96%.
[0073] The structure of the metal-free catalyst bislauryl peroxide is as follows:
[0074]
[0075] Comparative Example 7
[0076] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0077] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, azobisisovalerate (3.0 mmol) (a metal-free catalyst), propionaldehyde (6.5 mmol) (reducing agent), biphenyl (50.0 mg) (internal standard), acetonitrile (20.0 mL) (solvent), and propylene (10.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 29%, and the propylene oxide selectivity was 97%.
[0078] The metal-free catalyst azobisisovalerate has the following structural formula:
[0079]
[0080] Comparative Example 8
[0081] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0082] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, N-(2,3-epoxypropane)phthalamide (0.2 mmol), propionaldehyde (4.0 mmol), biphenyl (50.0 mg), acetonitrile (20.0 mL), and propylene (5.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 17%, and the propylene oxide selectivity was 94%.
[0083] The metal-free catalyst N-(2,3-epoxypropane)phthalamide has the following structural formula:
[0084]
[0085] Comparative Example 9
[0086] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0087] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, the following were added sequentially: a metal-free catalyst, nitric oxide radical piperidinol (0.4 mmol), a reducing agent, propionaldehyde (4.0 mmol), an internal standard, biphenyl (50.0 mg), a solvent, acetonitrile (20.0 mL), and propylene (6.0 mmol). The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 9%, and the propylene oxide selectivity was 96%.
[0088] The metal-free catalyst, nitric oxide radical piperidinol, has the following structural formula:
[0089]
[0090] Comparative Example 10
[0091] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0092] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, a dual metal-free catalyst (0 mmol), a reducing agent of propionaldehyde (4.0 mmol), an internal standard of biphenyl (50.0 mg), a solvent of acetonitrile (20.0 mL), and propylene (8.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 17%, and the propylene oxide selectivity was 96%.
[0093] Comparative Example 11
[0094] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0095] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, CoCl2 metal catalyst (0.3 mmol), propionaldehyde (4.0 mmol) as a reducing agent, biphenyl (50.0 mg) as an internal standard, acetonitrile (20.0 mL) as a solvent, and propylene (8.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 13%, and the propylene oxide selectivity was 95%.
[0096] Comparative Example 12
[0097] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0098] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, MnCl2 metal catalyst (0.3 mmol), propionaldehyde (4.0 mmol) as a reducing agent, biphenyl (50.0 mg) as an internal standard, acetonitrile (20.0 mL) as a solvent, and propylene (8.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion rate was found to be 22%, and the propylene oxide selectivity was 98%.
[0099] Comparative Example 13
[0100] A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst includes the following steps:
[0101] In a 100 mL stainless steel autoclave with a polytetrafluoroethylene liner, NiCl2 metal catalyst (0.3 mmol), propionaldehyde (4.0 mmol) as a reducing agent, biphenyl (50.0 mg) as an internal standard, acetonitrile (20.0 mL) as a solvent, and propylene (8.0 mmol) were added sequentially. The autoclave was then sealed, and air was introduced at 2 MPa. The reaction was stirred at 110 °C for 7 h. After the reaction was complete, the autoclave was cooled to -15 °C. After the vaporized organic matter in the autoclave was reliquefied, a sample was taken, filtered, and 1 mL of the sample was analyzed by gas chromatography. The propylene conversion was found to be 22%, and the propylene oxide selectivity was 98%.
Claims
1. A method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst, characterized in that, The dual metal-free catalyst and reducing agent were dispersed in a solvent, and propylene and air at 1-6.0 MPa were sequentially introduced into the closed system. The reaction was carried out at a set temperature of 40-120 °C for 1-9.0 h to obtain the product propylene oxide. The total molar amount of the dual metal-free catalyst and the molar ratio of propylene are 0.1-1:1-6.
0. The molar ratio of reducing agent to propylene is 5-15:1-10.
2. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The metal-free catalyst is any two of the compounds having the following structures; 。 3. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The reducing agent is one or two of acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, propionaldehyde, glutaraldehyde, n-hexanaldehyde, cyclohexeneformaldehyde, and benzaldehyde.
4. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The reaction temperature is 95-120 ℃.
5. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The total molar amount of the dual metal-free catalyst and the molar ratio of propylene are 0.3:3.5-6.
0.
6. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The molar ratio of the reducing agent to propylene is 9.5-12:3.5-6.
0.
7. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The reaction pressure is 2 MPa.
8. The method for preparing propylene oxide by air epoxidation catalyzed by a dual metal-free catalyst according to claim 1, characterized in that, The reaction time is 5.0-9.0 h.